Both a 6920 or BCM are great rifles. Chrome-lined 1:7 barrels, HP/MPI tested bolts and barrels.
Choose whichever rollmark you like best.
Forget the carry handle and look into an Aimpoint PRO with Magpul MBUS back up sights. http://www.sportoptics.com/aimpoint-pro-12841.aspx

The Aimpoints are very rugged and it is HIGHLY unlikely that you will be able to break it. (Check out the Daniel Defense torture test to see what an Aimpoint T-1 can handle.)
You also don't really need a rail. The Magpul MOE handguards will allow you to mount a vertical grip. http://store.magpul.com/prod_detail_list/184

That way you can decide if you really want/ need a quad rail. Don't really need a bipod on a 16 inch carbine, use your vertical grip or magazine as a monopod.
Just my opinion.